The field of invention is radio frequency identification (RFID) labels, more particularly a laminate label having an expandable layer.
RFID devices are known in the art, such as disclosed in U.S. Pat. No. 5,347,263. These devices are used in systems for access control, animal feeding and health programs, inventory control, process control, and security applications.
A typical RFID system has a passive RFID label having circuitry therein and a separate RFID reader/writer. The RFID reader/writer energizes the RFID label circuitry by transmitting a power signal. The power signal may convey data which is stored in memory incorporated in the RFID label circuitry. In response to the power signal the RFID label circuitry may transmit a response signal containing data stored in its memory. The RFID reader/writer receives the response signal and interprets the data contained therein. The data is then transmitted to a host computer for processing.
In order to minimize the cost of labels, the labels are fabricated in large quantities. One particular method of making the RFID label is to print a conductive material, such as silver conductive ink, in a pattern defining multiple antennae, onto a substrate. The ink may be printed using silk screening techniques, such as in a sheet fed or roll operation. Once the antennae are printed, each antenna is die cut into individual pieces. Each piece is placed in a carrier where an integrated circuit (IC) chip, such as a flip chip, is electrically connected to the antenna using conventional chip attachment methods. The chip is then encapsulated in an epoxy material and the entire assembly is sandwiched between protective layers.
This particular method of making an RFID label has several drawbacks. The substrate material is expensive and when die cut, there is significant waste. Once the individual antennae are die cut into individual pieces, each piece must be loaded into a carrier for subsequent processing. If a window is not cut into the substrate, when the chip is encapsulated, there is a bump on the label which can result in the chip being easily ripped off of the label rendering the label inoperative. Finally, the bump on the chip makes putting the label through marking equipment, such as thermal transfer, ink jet, or laser printers, difficult.
Another method of manufacturing an RFID label, described in U.S. Pat. No. 5,528,222, has an antenna formed as an integral part of an insulating substrate and a circuit chip mounted on the substrate. This particular label requires a substrate which increases the label thickness and the overall cost of the label. To minimize the label thickness, a window may be cut in the substrate allowing insertion of the chip into the window. Cutting a window in the substrate, however, further increases the cost of the label.